Update spelling "mbed TLS" to "Mbed TLS"

The official spelling of the trade mark changed from all-lowercase "mbed"
to normal proper noun capitalization "Mbed" a few years ago. We've been
using the new spelling in new text but still have the old spelling in a
lot of text. This commit updates most occurrences of "mbed TLS":

```
sed -i -e 's/mbed TLS/Mbed TLS/g' $(git ls-files ':!ChangeLog' ':!tests/data_files/**' ':!tests/suites/*.data' ':!programs/x509/*' ':!configs/tfm*')
```

Justification for the omissions:

* `ChangeLog`: historical text.
* `test/data_files/**`, `tests/suites/*.data`, `programs/x509/*`: many
  occurrences are significant names in certificates and such. Changing
  the spelling would invalidate many signatures and tests.
* `configs/tfm*`: this is an imported file. We'll follow the upstream
  updates.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index a3103d9..b134061 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -489,7 +489,7 @@
      * MBEDTLS_ECP_WINDOW_SIZE, as well as implementation details that may
      * change in the future. A factor 2 is a minimum safety margin.
      *
-     * For reference, with mbed TLS 2.4 and default settings, for P-256:
+     * For reference, with Mbed TLS 2.4 and default settings, for P-256:
      * - Random point mult:     ~3250M
      * - Cold base point mult:  ~3300M
      * - Hot base point mult:   ~1100M
diff --git a/tests/suites/test_suite_version.function b/tests/suites/test_suite_version.function
index 981f8ab..eeae512 100644
--- a/tests/suites/test_suite_version.function
+++ b/tests/suites/test_suite_version.function
@@ -20,7 +20,7 @@
     mbedtls_snprintf(build_str, 100, "%d.%d.%d", MBEDTLS_VERSION_MAJOR,
                      MBEDTLS_VERSION_MINOR, MBEDTLS_VERSION_PATCH);
 
-    mbedtls_snprintf(build_str_full, 100, "mbed TLS %d.%d.%d", MBEDTLS_VERSION_MAJOR,
+    mbedtls_snprintf(build_str_full, 100, "Mbed TLS %d.%d.%d", MBEDTLS_VERSION_MAJOR,
                      MBEDTLS_VERSION_MINOR, MBEDTLS_VERSION_PATCH);
 
     build_int = MBEDTLS_VERSION_MAJOR << 24 |
@@ -56,7 +56,7 @@
                      (get_int >> 24) & 0xFF,
                      (get_int >> 16) & 0xFF,
                      (get_int >> 8) & 0xFF);
-    mbedtls_snprintf(build_str_full, 100, "mbed TLS %s", version_str);
+    mbedtls_snprintf(build_str_full, 100, "Mbed TLS %s", version_str);
 
     TEST_ASSERT(strcmp(build_str, version_str) == 0);
     TEST_ASSERT(strcmp(build_str_full, get_str_full) == 0);
diff --git a/tests/suites/test_suite_x509parse.function b/tests/suites/test_suite_x509parse.function
index 09a9d12..6e32792 100644
--- a/tests/suites/test_suite_x509parse.function
+++ b/tests/suites/test_suite_x509parse.function
@@ -564,7 +564,7 @@
     /*
      * See comments on ecp_test_vect_restart() for op count precision.
      *
-     * For reference, with mbed TLS 2.6 and default settings:
+     * For reference, with Mbed TLS 2.6 and default settings:
      * - ecdsa_verify() for P-256:  ~  6700
      * - ecdsa_verify() for P-384:  ~ 18800
      * - x509_verify() for server5 -> test-ca2:             ~ 18800